Create a Linq expression using StartsWith, EndsWith and Contains the transmission of the expression <Func <T, string >>

Question

I want to create a method that passes an expression of type Expression<Func<T, string> to create an expression of type Expression<Func<T, bool>> to filter the property of a string using the StartsWith , EndsWith and Contains methods similar to these expressions:

 .Where(e => e.MiProperty.ToUpper().StartsWith("ABC")); .Where(e => e.MiProperty.ToUpper().EndsWith("XYZ")); .Where(e => e.MiProperty.ToUpper().Contains("MNO")); 

the method should look like this:

 public Expression<Func<T, bool>> AddFilterToStringProperty<T>(Expresssion<Func<T, string>> pMyExpression, string pFilter, FilterType pFiltertype) 

where FilterType is an enumeration type that contains three of the mentioned operations ( StartsWith , EndsWith , Contains )

Answer 1

Try the following:

 public static Expression<Func<T, bool>> AddFilterToStringProperty<T>( Expression<Func<T, string>> expression, string filter, FilterType type) { return Expression.Lambda<Func<T, bool>>( Expression.Call( expression.Body, type.ToString(), null, Expression.Constant(filter)), expression.Parameters); } 

Answer 2

Thanks @dtb. It works fine, and I added the expression "not null" for this case:

 public static Expression<Func<T, bool>> AddFilterToStringProperty2<T>( Expression<Func<T, string>> expression, string filter, FilterType type) { var vNotNullExpresion = Expression.NotEqual( expression.Body, Expression.Constant(null)); var vMethodExpresion = Expression.Call( expression.Body, type.ToString(), null, Expression.Constant(filter)); var vFilterExpresion = Expression.AndAlso(vNotNullExpresion, vMethodExpresion); return Expression.Lambda<Func<T, bool>>( vFilterExpresion, expression.Parameters); }